Battery drains completely down
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
You know enough to test the alternator now, basically. Maybe better than AutoZone or Sears?
What's the temperature?
First start with a fully charged battery. A cold battery is tougher to charge (internal resistance) than in hot weather. What confused me at first during troubleshooting was the vehicle (at least off idle) isn't running off the battery at all, whether alternator or generator. The battery is basically a filter, and primarily for starting or the radio when parked. Other than that the charging system carries the load.
Figure 5 amps (each) for headlights, maybe 5 amps for the ignition? So if there's any problem with charging it will show up quick. Just a start cycle for a split second with even a healthy starter will really draw a battery down. If the battery reads 12.5 at rest that's about a 75 per cent charge. If it's even chilly and the battery is weak, headlights, then you're going to want to see closer to 15 volts for a while at say 1500 RPM and then it will settle down.
What's the temperature?
First start with a fully charged battery. A cold battery is tougher to charge (internal resistance) than in hot weather. What confused me at first during troubleshooting was the vehicle (at least off idle) isn't running off the battery at all, whether alternator or generator. The battery is basically a filter, and primarily for starting or the radio when parked. Other than that the charging system carries the load.
Figure 5 amps (each) for headlights, maybe 5 amps for the ignition? So if there's any problem with charging it will show up quick. Just a start cycle for a split second with even a healthy starter will really draw a battery down. If the battery reads 12.5 at rest that's about a 75 per cent charge. If it's even chilly and the battery is weak, headlights, then you're going to want to see closer to 15 volts for a while at say 1500 RPM and then it will settle down.
FTE fan
Joined: Dec 2006
Posts: 3,674
Likes: 11
From: paradise, northern calif.
A lot of good information from a lot of smart people so far . One thing I didn't notice being mentioned is, use caution around a charging battery. For sure on the water/acid type of battery (I'm not so sure on the Gell or optima rap type). A charging battery will give off explosive gas, so be very carful, use eye protection, and make sure your last connection is the negative to the frame while testing(with a jumper if necessary)to keep any spark away from any source of battery gassing. I saw a guy blow up a battery while charging it. Im no expert so if any one cares to elaborate on this part of it please go for it, it wont hurt my feelings. Safety first.Good luck
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Not just sulfuric fumes or dangerous fire/explosion hazards, also just plain toxic gases that are not good to breathe.
If a battery is kept charged though, it doesn't need to spend hours and hours charging, if that makes any sense, and the fumes will be minimized.
If a battery is kept charged though, it doesn't need to spend hours and hours charging, if that makes any sense, and the fumes will be minimized.
Fleet Mechanic
Joined: Dec 2005
Posts: 1,603
Likes: 44
Just a thought, I have one truck being a 1954 F900, still has the Lincoln
but was converted to 12vt positive ground with a big 100amp Leece Neville
alternator (this was done back who knows when) I had to install cole hershey disconnect switch on the floor (all my big jobs got them) so one
day and overnite the battery is dead. The parasite is the alternator with
internal regulator. I think its going to get a one wire 90 amp neg ground
alternator, but I just dread flipping the wire on the ampmeter cause of all
the air lines and no room and the jungles of wires previous owners did
(no problem its called side snips) and also my tip is, on all my trucks when
I freshed up under the dash, I added two feet to the instrument cluster
with a disconnect, only thing to disconnect is speedo cable and place the
whole cluster on your lap. Why? its to get at the dispicable wiper linkage.
but was converted to 12vt positive ground with a big 100amp Leece Neville
alternator (this was done back who knows when) I had to install cole hershey disconnect switch on the floor (all my big jobs got them) so one
day and overnite the battery is dead. The parasite is the alternator with
internal regulator. I think its going to get a one wire 90 amp neg ground
alternator, but I just dread flipping the wire on the ampmeter cause of all
the air lines and no room and the jungles of wires previous owners did
(no problem its called side snips) and also my tip is, on all my trucks when
I freshed up under the dash, I added two feet to the instrument cluster
with a disconnect, only thing to disconnect is speedo cable and place the
whole cluster on your lap. Why? its to get at the dispicable wiper linkage.
Post Fiend
Joined: Sep 2006
Posts: 14,325
Likes: 14
From: Island Southeast Alaska
With out any computerized fuel injection chit on your truck it won't hurt to pull
off the Neg cable while it is running. If it dies when this is done that it ain't charging.
It's as simple as that.
off the Neg cable while it is running. If it dies when this is done that it ain't charging.
It's as simple as that.
Fleet Owner
Joined: Jul 2004
Posts: 27,294
Likes: 1,055
From: NM
That isn't a good idea with some alternators, they need the battery for reference voltage.
Post Fiend
Joined: Sep 2006
Posts: 14,325
Likes: 14
From: Island Southeast Alaska
style alt that I have yet to see. What will happen if it has that style of alt
on it? I can not for the life of me think what it could damage. The alt?
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Logistics Pro
Joined: Nov 2011
Posts: 4,685
Likes: 80
From: Northville, MI
No, the engine won't die until the battery power drops below the voltage necessary to run the ignition system. That voltage is nowhere close to what you need to run your starter. I'm not sure what year truck you have but if your ammeter works you can tell from that when you have a negative draw. If you have no ammeter then as others have recommended I would get your generator output checked.
Fleet Owner
Joined: Jul 2004
Posts: 27,294
Likes: 1,055
From: NM
Like the post by "Angry Corvair Super Dork" (LOL) says, a 3-wire type alternator adjusts output by looking at system voltage. If it doesn't see a battery voltage, it ramps up output thinking the battery is way low. It "may" fry the regulator or components of the car due to overvoltage.
Thread Starter
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Senior User
Joined: Sep 2013
Posts: 269
Likes: 2
From: Abingdon. VA
Wow, with all the possible options and possible hazards for a slow burning candle like me, I am worried about screwing up more things and more important things in trying to find the problem. What are the major problems I need to avoid? I blew out some electrical with the brake lights trying to find a short once before so I have experience in screwing up. At least I can charge it now and have it run.
Thread Starter
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Senior User
Joined: Sep 2013
Posts: 269
Likes: 2
From: Abingdon. VA
One wire alternator.
Believe Nothing
Joined: Jun 2004
Posts: 7,514
Likes: 398
From: W. Central FL.
Wow, with all the possible options and possible hazards for a slow burning candle like me, I am worried about screwing up more things and more important things in trying to find the problem. What are the major problems I need to avoid? I blew out some electrical with the brake lights trying to find a short once before so I have experience in screwing up. At least I can charge it now and have it run.
1. Obtain a volt meter. Lowes, HD, many places sell in expensive meters. Playing with an old truck, you need a meter. An alligator clip is needed for the leads or someone to help with this exercise is recommended .
2. Set meter to DC volt scale.
3. Put positive meter lead on positive post of battery.
4. Put negative meter lead on negative terminal of battery.
5. Note reading of meter....Should be around 12.5 volts.
6. Start vehicle.
7. Raise engine speed a few hundred RPM or more.
8. Repeat steps 3 thru 4.
9. Meter should show more than 12.5 V and less than 15 V. if the generator or alternator is working.
FTE Chapter Leader
Joined: Dec 2001
Posts: 3,636
Likes: 11
From: Crossville, Tn
Don't know if this will apply here. When I first got Edith back together, I found that if she sat for a week or more it drained the battery down to where I didn't have enough to start her. It took me a day to find the culprit, when I installed the one wire alternator, I installed a volt meter in place of the amp meter. I connected the meter directly to the alternator and found that when the truck was not running, the meter was drawing indirectly from the battery.